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We’ve covered 13 presidential elections, and based on that background, we remain convinced that neither Trump nor Sanders will win his party’s nomination – let alone the White House.

We have seen these “surges” many times before. Voters take a summer fling with a new and seductive romance. But when it comes time to settle down, to pick a partner for the long haul, to vote for someone who might actually be president, their mood changes.

They ditch the summer stranger and turn to a candidate who has the character, temperament and qualifications to be a plausible occupant of the Oval Office. They might keep a small photo of their old flame tucked away somewhere. But he’s not on their mantelpiece. Or in their future.

Of course, we could be wrong. This year could be totally different. Voters could be so deeply disenchanted that they defy traditional patterns and run off with the outlander. But so far the evidence does not point that way.

Start with Sanders. Give him credit for running an energetic campaign that fires up supporters in a way that Clinton or Jeb Bush can only dream about. As one of his volunteers in Iowa told The New York Times, “I feel a part of something.”

But the Sanders surge is fueled mainly by two factors outside his control.

First, liberals have always distrusted the Clintons as pragmatic heretics who pioneered a “Third Way” while proclaiming “the era of Big Government is over.” Bill Clinton’s departure from left-wing orthodoxy was a key reason why he became the first Democrat since Roosevelt to win two presidential elections, but his success only made liberals more resentful.

Secondly, Hillary has run a poor campaign, fumbling the email server issue and failing to generate any real passion or loyalty.

“I used to like her, but I don’t trust her,” Donald Walters of Louisville, Kentucky, told AP. “Ever since she’s announced her candidacy for president, I just haven’t liked the way she’s handled things. She doesn’t answer questions directly.”

Despite those factors, the latest Public Policy poll still shows Clinton leading Sanders by 35 points nationally. Just three weeks after New Hampshire, on Super Tuesday, 12 states will hold primaries or caucuses. It’s hard to see how Sanders has anything like the resources to compete with Clinton on that scale.

Besides, Sanders will be 75 on Election Day. He’s a self-described socialist, while only 24 percent of Americans called themselves liberals in the latest Gallup Poll. Is the Democratic Party really ready to commit suicide? To concede the White House while Republicans already control Congress?

The Republican story is murkier. Trump is an extremely clever showman, a deft demagogue who understands modern media and uses it to manipulate emotions and appeal to America’s darker and uglier instincts. Fear the foreigner! Whatever your problem is, blame the Mexican rapist! The Chinese worker! The Muslim plotter!

In the Public Policy poll, two-thirds of Trump’s supporters say President Obama is a Muslim. Three out of five say he was not born in the United States and want to amend the Constitution to eliminate birthright citizenship. We use the word “racism” very carefully, but we know it when we see it. And Trumpeters hear his coded signals loud and clear.

Like Sanders, Trump profits from a team of underwhelming rivals. Jeb Bush has been particularly disappointing, but now, finally, he seems ready to take on Trump; perhaps other Republicans will be emboldened to join in.

Next year, the electorate will be only 70 percent white. Nominating a candidate who drives away immigrants and voters of color would spell absolute disaster for the Republican Party. It’s hard to believe they want to commit suicide, either.

All of our experience and instincts tell us that as the weather gets colder and the primaries get closer, the summer romances will dim, the surges will slow, the strangers will fade.

It hasn’t happened yet. And this year could truly be different. But don’t bet on it. Yet.

Steve and Cokie Roberts can be contacted by email at stevecokie@gmail.com.